Initializing Nasal early

The position init code is a little complex, to allow for starting on a carrier and some other cases, and ideally we would do it from script, but unfortunately there's some technical limitations on doing that. (Not insurmountable, but not quick either). Adding more cases to the position-init code is certainly doable - one suggestion I made some time ago, is when MP is active, to default to starting at a free parking position instead of on a runway. (When no startup position is provided at all). This would avoid people accidentally starting on the runway in MP events, which would be a big usability win. When no parking positions are defined, AI traffic defaults to the 'airport centre' location. Selection a taxiway parallel to the active runway is possible, but for complex airport layouts I can imagine many ways this logic could fail. Personally I think it would be more robust to stick to picking parking positions, and otherwise using the airport centre, because it would encourage people to add the parking position data :) I anyone wants to work on this, it would be a self-contained function in position-init code, just ask here for any questions. All the pieces certainly exist - the taxiways, parking locations and runways for the airport are all accessible. — James Turner

I would prefer to init Nasal earlier in startup, because I would like use Canvas-based UI for pieces such as aircraft-selection - but right now we have to load Nasal in postInit, which is seconds and seconds into startup. Most Nasal things that need FDM state already wait on fdm-initialized, so in theory the only fix required is to skip <nasal> evaluation in 'animation' XML files (apparently there is a long-standing assumption that such elements are skipped when loading an aircraft as the main one, i.e they are only run for AI / MP aircraft - this is a bad situation but changing it now could be a serious compatibility problem) — zakalawe (Sun Oct 27). Re: Modular Nasal . (powered by Instant-Cquotes)

For the sake of simplicity, we could refactor the ::init() method such that the common init code could be shared, between the initial startup Nasal interpreter, and the final runtime interpreter - so that we could load init code from a separate $FG_ROOT directory to do such things, without parsing all the stuff in $FG_ROOT/Nasal.

Referring to the GLSL segfault fix and my earlier comment about defaulting to a NON-SHADER environment by adjusting shader quality level to 0 if shaders are unsupported: For now, this is obviously easy to simply hard-code by showing an ALERT message and overriding the shader settings from there on.

However, in the long run, we'd probably want to simply delegate such stuff to Nasal space. While Nasal is currently not available that early, we could use a bare (or just temporary) Nasal instance during initialization to hand-off such stuff to scripting space. This seems to be an old idea actually (see the comments below from 2008) - and peopel were actually working on having Nasal + GUI code up really early back in 2008.

Given the state of the current init code in fg_init.cxx, the idea of factoring stuff out into Nasal space is very appealing - which means having less unmaintained C++ spaghetti code, and things like processing startup arguments can be really easily done from Nasal space, what's needed is "only" the props code - or rather just setprop/getprop, which would allow simple logic to be moved to scripting space - and it would not even be performance-critical.

In other words, it would be sensible to pick up the old idea and make a minimal Nasal interpreter available early on, and pass control to it - so that things like thís can be easily run, without hard-coding any logic:

if (getprop("/sim/rendering/gl-shading-language-version")=="UNSUPPORTED") {
print("Warning: Shaders unavailable, defaulting to quality level 0!\n")
setprop("/sim/rendering/shaders/quality-level", 0);
}

The only catch is, subsystems are initialised late, but I need a handful to be up before I can use the GUI dialogs; obviously the GUI subsystem itself, but also Nasal and a few others. (There are some issues with initialising nasal early, it is currently deliberately being done very late, but more on that later...) — James Turner

I would appreciate if Nasal were around the first subsystems to be initialized. But this would require some Nasal dependency resolution. Almost all Nasal code needs globals.nas, and most need props.nas, too (which needs globals.nas). gui.nas needs globals.nas and props.nas, and screen.nas needs all three etc. This needs to be taken care of if Nasal is to be initialized early. — Melchior FRANZ

starting up the interpreter (the first part of  FGNasalSys::init) can be done very early (and quickly), and the subsytem would then wait for a relatively high-valued 'init' call before running scripts (the part that needs all other properties to be defined). — James Turner

I'm sure other people can propose potential groups, but I'd imagine: early (nasal itself, GUI) time based subsystems (ephemeris, datetime, warp, properties, interpolator) environmental (weather fetch) aircraft systems (FDM, electrical, cockpit?, instruments, failures, GPS) scenery (tile manager, views, panels) input  IO subsystems - ATC, traffic, multiplayer sound — James Turner

I will start the systems I need (Nasal, GUI and input) early. This might also help make the startup progress a bit more fine-grained. — James Turner

In the even longer run, we'd actually want to associate the Nasal scripts with run-levels (/etc/rc.d, anyone?), since the frontend GUI might want a few scripts loaded, while I assume most are only relevant when actually flying. Such a change also makes postinit() unnecessary, I think - since the effect can always be achieved by having init() watch for a higher run-level. — James Turner